Flexural Strength of Reinforced and Prestressed Concrete T-Beams 44 PCI JOURNAL Stephen J. Seguirant, P.E. Vice President and Director of Engineering Concrete Technology Corporation Tacoma, Washington Bijan Khaleghi, Ph.D., P.E. Concrete Specialist Bridge & Structures Office Washington State Department of Transportation Olympia, Washington Richard Brice, P.E. Bridge Software Engineer Bridge & Structures Office Washington State Department of Transportation Olympia, Washington The calculation of the flexural strength of concrete T-beams has been extensively discussed in recent issues of the PCI JOURNAL. The debate centers on when T-beam behavior is assumed to begin. The AASHTO LRFD Bridge Design Specifications (LRFD) maintain that it begins when c (distance from extreme compression fiber to neutral axis) exceeds the thickness of the flange. The AASHTO Standard Specifications for Highway Bridges (STD), and other references, contend that it begins when a (depth of equivalent rectangular stress block) ex- ceeds the flange thickness. This paper examines the fundamentals of T-beam behavior at nominal flex- ural strength, and compares the results of LRFD and STD with more rigorous analyses, including the PCI Bridge Design Manual (PCI BDM) method and a strain compatibility approach using nonlinear concrete compressive stress distributions. For pre- tensioned T-beams of uniform strength, a method consisting of a mixture of LRFD and STD is investi- gated. For T-beams with different concrete strengths in the flange and web, the PCI BDM method is com- pared with the nonlinear strain compatibility analy- sis. High strength concretes (HSC) up to 15,000 psi (103 MPa) are considered. The selection of appro- priate φ factors and maximum reinforcement limits is also discussed. Comparisons with previous tests of T-beams are presented, and revisions to the rel- evant sections of LRFD are proposed.
Flexural Strength of Reinforced and Prestressed Concrete T-Beams
Jun 18, 2023
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